The present invention generally relates to fabrication of semiconductor devices and more particularly to a rapid thermal processing apparatus.
The art of rapid thermal processing (RTP) includes the processes such as rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD), rapid thermal oxidation (RTO), rapid thermal nitridation (RTN), and the like, and is used extensively in the fabrication process of semiconductor devices including memory integrated circuits and logic integrated circuits.
A typical fabrication process of a semiconductor integrated circuit includes various thermal process steps such as film deposition, annealing, oxidation, diffusion, sputtering, etching, nitridation, and the like. Thus, a semiconductor substrate is subjected to a number of such thermal process steps.
An RTP process is a promising substrate processing for improving the yield and quality of semiconductor devices, in view of the fact that the temperature rise and fall are carried out in a short time period at a very large rate. By using an RTP process, the duration in which the substrate is subjected to a high temperature is reduced substantially.
A conventional RTP apparatus generally includes a cluster-type processing chamber for a single-wafer processing of a substrate, wherein the substrate may be a semiconductor wafer, a glass substrate carrying a photomask, a glass substrate for a liquid crystal display device, a substrate for an optical disk, and the like. The processing chamber has a quartz window and a high-power lamp such as a halogen lamp is disposed adjacent to the quartz window on and/or below the processing chamber so as to heat the substrate in the processing chamber through the quartz window. The lamp carries a reflector at the side opposite to the side in which the substrate is located.
Typically, the quartz window is formed to have a plate-like form, while a tubular-form window is also possible. In the latter case, the substrate to be processed is accommodated in the tubular quartz window. In the event the processing chamber is evacuated by a vacuum pump, it is preferable to form the quartz window to have a thickness of several ten millimeters (30-40 mm) so as to secure a sufficient mechanical strength for bearing the atmospheric pressure applied to the evacuated processing chamber. In view of the tendency that a thermal stress causes the quartz window to be concaved toward the interior of the processing chamber, there are cases in which the quartz window is provided with a compensating convex curve such that the quartz window projects outward from the processing chamber.
In order to achieve a uniform heating, a number of halogen lamps are arranged adjacent to the quartz window, wherein the thermal radiation produced by the halogen lamps are directed toward the substrate in the processing chamber by the reflector provided behind the halogen lamps. Typically, the processing chamber has a gate valve on the sidewall thereof for in-and-out operation of the substrate, and a gas supply nozzle is provided also on the sidewall of the processing chamber.
In such an RTP apparatus, it is important to measure the substrate temperature accurately for achieving reliable processing. For this purpose, there is provided a temperature detector on the processing chamber such that the temperature detector detects the temperature of the substrate in the processing chamber. While such a temperature detector can be formed by a thermocouple, the use of a thermocouple is not preferable in an RTP apparatus as there is a possibility that the metal constituting the thermocouple may cause a contamination of the substrate.
In view of the situation noted above, conventional RTP apparatuses have used a radiation pyrometer for temperature detection of the substrate, wherein such a radiation thermometer or pyrometer detects the strength of the thermal radiation emitted from the rear surface of the substrate. The thermal radiation strength thus detected is converted to temperature based on the emissivity xcex5 according to the relationship
Em(T)=xcex5EBB(T)xe2x80x83xe2x80x83(1) 
wherein Em (T) represents the detected radiation strength while EBB (T) represents the radiation strength of a black body at the temperature T. The use of such a pyrometer is already disclosed in Japanese Laid-Open Patent Publication 11-258051.
In operation of the RTP apparatus, a wafer to be processed is introduced into the processing chamber and is held on a wafer stage by a chuck mechanism. Further, a processing gas such as a nitrogen gas or oxygen gas is introduced into the processing chamber from the gas supply nozzle, and the halogen lamp is energized for rapid heating of the wafer. Thereby, the temperature of the substrate is detected by the radiation pyrometer and a controller controlling the energization of the halogen lamp achieves a feedback control in response to the output of the radiation pyrometer.
On the other hand, such a conventional RTP apparatus using a radiation pyrometer has a drawback in that, because of the small distance between the substrate and the sensing head of the pyrometer, there occurs a temperature rise in the sensing head of the pyrometer as a result of thermal radiation from the wafer and an error is introduced into the result of the temperature detection.
While such an error can be avoided by providing a cooling fixture to the pyrometer, such a construction increases the size and cost of the RTP apparatus.
Further, the conventional RTP apparatus using a radiation pyrometer for the temperature detection of the substrate has suffered from the problem of low accuracy of temperature measurement, wherein it was discovered that the problem has been caused not only by the foregoing temperature rise of the pyrometer but also by other reasons.
As a result of investigation constituting the foundation of the present invention, the inventor of the present invention has discovered that there occurs a deviation in the Eq. (1) noted before, provided that: (1) the sensing head of the pyrometer detects multiple reflection of the thermal radiation emitted by the substrate; (2) there is a thermal radiation coming in from a heat source other than the target region of the wafer; (3) there is a reflection loss at the end surface of the optical medium interposed between the wafer and the sensing head; and (4) there is a substantial absorption loss in the optical medium. In the case of the RTP apparatus, in which a reflective coating is provided on various parts of the processing chamber for improving the thermal efficiency, the effect of the foregoing factors (1) and (2) cannot be ignored.
Accordingly, it is a general object of the present invention to provide a novel and useful thermal processing apparatus wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a thermal processing apparatus wherein accuracy of temperature detection is improved.
Another object of the present invention is to provide an improved temperature detection method for a thermal processing apparatus wherein the factors causing a detection error are taken into consideration and the detection error is eliminated.
Another object of the present invention is to provide a method of detecting a temperature of an object disposed in a multiple-reflection environment by way of a radiation pyrometer, comprising the steps of:
detecting a radiation strength emitted from a target region of said object;
applying a correction to said radiation strength so as to compensate for the effect of multiple reflections of a radiation emitted from said object;
applying a correction to said radiation strength so as to compensate for a reflection loss caused at an end surface of an optical medium interposed between said object and said sensing head;
applying a correction to said radiation strength so as to compensate for an optical absorption loss caused in said optical medium; and
applying a correction to said radiation strength so as to compensate for a stray radiation coming in to said sensing head from a source other than said target region of said object.
According to the present invention, the deviation of the temperature detected by the pyrometer from the true temperature is effectively compensated for with regard to: the multiple reflections taking place in the multiple reflection environment; the reflection loss at the surface of the optical medium between the substrate and the sensing head; the absorption loss in the optical medium; and the stray thermal radiation coming in to the sensing head from a source other than the target region of the object. The object may be a substrate or a wafer and the multiple-reflection environment may be a processing chamber of a thermal processing apparatus. Thus, an accurate temperature measurement becomes possible in a thermal processing apparatus by using a pyrometer, and the temperature control in such a thermal processing apparatus is improved.
Another object of the present invention is to provide a thermal processing apparatus, comprising:
a processing chamber including therein a stage adapted for supporting a substrate thereon, said processing chamber having an evacuation port for connection to an evacuation system;
a heat source provided so as to heat said substrate in said processing chamber;
a radiation pyrometer coupled to said processing chamber for measurement of a temperature of said substrate;
a control unit for controlling energization of said heat source in response to a temperature of said substrate; and
a cooling mechanism for cooling a part of said processing chamber in the vicinity of said radiation pyrometer,
said radiation pyrometer comprising:
a rotary chopper having a slit and a high-reflective surface and a low-reflective region, said rotary chopper being disposed in an optical path of a radiation emitted from said substrate;
a transparent rod disposed in said optical path between said substrate and said chopper, said transparent rod allowing a multiple reflection of said radiation between said wafer and said chopper; and
a detector disposed behind said chopper for detecting said radiation passed through said slit.
According to the present invention, the distance between the detector and the substrate is increased, and the effect of temperature rise of the detector and associated deviation of the temperature detection are successfully avoided.
Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings.